The invention relates to a method for adjusting a multilevel phase-shifting mask or a multilevel phase-shifting reticle with the aid of at least one alignment mark applied to the mask or the reticle.
The basis for exposing the levels of a multilevel phase-shifting mask is the correct alignment with alignment structures. Raster-scanning of the mask/reticle to find these alignment structures with the aid of an electron beam has so far not been possible because of the electric charging of the substrate irradiated with charged particles, or has led to unreliable adjustments because of a reduction in the resolution. Optical recognition of the alignment marks is not possible with the required resolution for future generations of technology.
So far, alignment marks that have been optically evaluated with the aid of a laser beam starting from the second level during exposure have been written in the first exposure step of the mask or the reticle.
It is accordingly an object of the invention to provide a method for adjusting a multilevel phase-shifting mask or a multilevel phase-shifting reticle that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that renders possible the detection of alignment marks with a very high accuracy with the aid of charged and uncharged particle or photon beams, and, thereby, renders possible a very accurate positioning of a plurality of levels of a mask or a reticle one above another.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for adjusting a mask device, including the steps of, in a first step, before a first exposure of a mask device having a substrate, one of applying at least two alignment marks onto the substrate of the mask device and introducing at least two alignment marks into the substrate of the mask device, and, in a second step, coating at least the alignment marks and regions immediately surrounding the alignment marks with a conducting layer and raster-scanning the alignment marks for all following alignment steps of a plurality of mask levels with a beam selected from at least one of the group consisting of an uncharged particle beam, a charged particle beam, an uncharged photon beam, and a charged photon beam.
In accordance with a significant aspect of the invention, an adjusting method that achieves the above object is distinguished in that at least two alignment marks are applied or introduced onto or into the substrate of the mask or of the reticle in a first step before the first exposure step of the mask or of the reticle, in that, in a second step, at least the alignment marks produced in the first step and the regions immediately surrounding them are coated with a thin conducting layer, and in that, for all following alignment steps of the plurality of mask levels, these alignment marks applied in the first step are raster-scanned with an uncharged or charged particle or photon beam. Preferably, the mask device is a multilevel phase-shifting mask or a multilevel phase-shifting reticle.
In accordance with another feature of the invention, the same particle or photon beam is preferably and advantageously used for the alignment steps as for the exposure. The invention preferably uses an electron beam as the particle beam.
In accordance with a further mode of the invention, the dose and the current density of the particle or photon beam used for the raster-scanning of the alignment marks applied in the first step is set substantially lower than in the case of the exposure steps of the mask or of the reticle.
In accordance with an added mode of the invention, the thin conducting layer is preferably grounded during the raster-scanning of the alignment marks.
The thin conducting layer can, preferably, be applied over the whole surface of the substrate, that is to say, including over the previously exposed alignment marks. The configuration renders it possible for the manufacturer of the mask blank to supply the latter with the alignment marks and the thin conducting layer applied thereover.
In accordance with a concomitant mode of the invention, in the first step, the alignment marks can, for example, be etched into the substrate or, alternatively, also deposited thereon.
Overall, the present invention renders possible the detection of alignment marks, applied to the substrate or introduced into the substrate before the first exposure step, with a very high accuracy with the aid of charged and uncharged particle or photon beams, and, thereby, renders possible a very accurate positioning of a plurality of levels of a mask or a reticle one above another.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for adjusting a multilevel phase-shifting mask, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.